Final fantasy XIV ARR was released August 27, 2013. Fact.
WoW had roughly 10 mil subs during last years beginning. Fact.
Wow has been dropping exponentially since then. Also fact.
http://www.maximumpc.com/world_warcr...n_players_2013
Considering maybe people look for an mmo after leaving another one (which is common knowledge and practice) it is safe to assume they saw arr, decided to come to this game and walla!
Considering the drop in people logging in. (different for each guild) ITs safe to assume there's some fall in the subscription base.
So as you can see my friend, its far from conjecture. Some fact and some easy observation and a little bit of common sense (aka no rose colored glasses).